Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 10 Counting Methods and Probability - 10.2 Use Combinations and Binomial Theorem - 10.2 Exercises - Skill Practice - Page 695: 39


See below.

Work Step by Step

Since the ordering doesn't matter in the selection, we use combinations. $_nP_r=\frac{n!}{(n-r)!}$, hence here: $_{12}P_2=\frac{12!}{(12-2)!}=\frac{12!}{10!}=12\cdot11=132$ We know that $_nC_r=\frac{n!}{r!(n-r)!}$. Hence $_{280}C_5=\frac{280!}{5!275!}=13836130056$
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